Ultra high frequency dielectric heater



1949- H. E. REVERCOMB ET AL 2,433,933

ULTRA HIGH FREQUENCY DIELECTRIC HEATER Filed Oct. 15, 1947 HIGH FREQUENCY l I #25 Inventors Henry Earl Revercomb,

Philip W. Morse, by, W%)ZMT Their" Attorney.

Patented Oct. 4, 1949 ULTRA HIGH FREQUENCY DIELECTRIC HEATER Henry, Earl Revercomb, North-.- Syracuse, and

Philip W. Morse, Glay, N. Y., assignors to General Electric Company, a..corp,ora.tion-of. New.

York

Application October 15, 1947, Serial No.1 779,940v

3 Claims. 1

Our invention relates to ultrahigh frequency dielectric heaters, more particularly to. such heaters employing a cavity or chamberof conducting. material in which standing electromagneticwaves are produced, andhas for its object aheater for continuously and uniformly heating thin sheets or cords of dielectric ma-. terial.

In carryingout our. invention in one form, We utilize: a cavity or chamberof such size relative to the wave length ofthe-high frequency source that a. transverse-electric field mode is produced in the chamber, together with a set of rollers on each side of the chamber for passing a strip or sheet material back andiforth across the chamber'in a direction either perpendicular, parallel, or at an obliqueangle to theelectric field whereby uniform heating by the. electric field is obtained. Moreover, we. mount the entrance roller and the exit roller at a slight angle withthe axis of the cavity in such manner asgraduallyito move or shift themateriallengthwise .of the cavity for substantially a half Wave length in order to give.-

uniform heating by. standing electromagnetic waves in the chamber.

For a more. complete: understanding of 'our. invention reference shouldibe hadto the accome panying drawing, Fig. 1 of which is a plane view. of. an ultra highv frequency. heater embodying,

our invention, Fig. 2 is a sectionalzview taken.

along the.1ine*2-'-2. of Fig; 1 look-ingsin :the. direce tion of the arrow, while Fig. 3 is asectional View similar to Fig. 2 showing a modified form ofzour. invention.

Referring to the drawing, we have shown our invention in one form as applied to the heating for drying purposes-or otherwise of'a thin strip or sheet I of dielectric material such as rubber, textile material, or cellulose material. It will be understood, however, that the sheet may comprise a large number of cords or threads positioned-side by side and simulating a sheet.

As shown in the drawing, theheater comprises an elongated rectangular cavity or chamber'Z formed from, thin walls of highly conducting material such as copper. High frequency'power. is supplied tooneend. of the cavity 2 from a suitable source 3 at a suitable ultra high frequency, suchas 1000 megacycles, by suitable means shownas a co-axial supplyline consisting of an outer tubular conductor 4 electrically connected to one end 'of the longer transverse side wall'of th'e chamber andan inner conductor or probe 5 which extends into the chamber. The conductors 4 and 5 are electrically insulated frornseach other, andareperpendicular tosthe longer side wall of the-chamber.

chamber.

Wepreaferably construct the chamberi of such. size with relationto the wave length of-theihigh' frequency supply source that a transverse electric, field.- 1n ode Hm,n,p is produced-in the chamber,- i. an electric field whose corn-ponentsorvecs tors lie entirely in. planes transverse tethechanher.- spscify the number of halfsinusoidal electric ver-iationsein the-three dimensions onwalls, of the chamber indicated .by -these,letters on the.

drawing;

More. specifically. we preferably use a tr-anss This mode requires a short transverse. dimension or side m whichis. less than one-half of-the wave. length in thechamberduringthe-heating operation.

verse-electric fieldumode Ho,l,p.

when-the-chamber containsthe sheet I being heated; hereinafter referred to as a. loaded.

chamber. Also, this anode requires a long -transverseedirnension or-siden which isless thanone wave --lengthxexisting--in the loaded chamber but somewhat more than one-halfwave: length; Prefierably.thesclistance 8 between the two -paral-. lelsets of parallel rollers 9i and: It) is made greater: thanone-half wave length.' The length: of the -chamber isat least several wave lengths... Standing electromagnetic wavesare, therefore,

produced: in' the chamber.

Inview ofthe-fact that the transverse elec-.- tricfield; as indicated by the-arrows-in Fig. 2, is confined to.=a-=distance -ofronehalf wave length;

between-the sets of rollers' fi and-ill, the sets of rollers are-positioned on opposite sides substantial-ly outside or the electric field whereby heatleg or ollersis minimized.

stantially horizontal lengths l 2; as seen in Fig; 2 extending Lsubstantiallyrparallel with the longer side wallmz Fivesuch lengths l2 are shown, tow

gather with a sixth length made up of two halves l3 "and l 4 at r the l entrance and exit points of the material, at which points oblique slots l5i and. I61

are. provideclrfor the sheet. inthe walls ofthe chamber. Th'e'sets:of1rollers-:9.and lilare made ofia suitable. low loss dielectric;.material:or1 a.

good electrically conducting material such as The: probe. 5-: is parallel with the. electric field produced in they In his mode-.theletters m, and p copper, preferably the latter. Each set is suitably supported on brackets mounted in the chamber adjacent the shorter side walls. As shown, the set 10 is mounted on brackets I! and I8, similar brackets being provided for the set of rollers 9. Guide rollers I9 and 20 are provided adjacent the entrance and exit openings.

It will be observed that in Fig. 2 the cross lengths l2 of the sheet pass each a number of times, depending upon the number of passes, through the transverse electric field indicated by the arrows, which electric field is a maximum value at the middle and a minimum value at each side.

For the purpose of producing uniform heating in the sheet at all points crosswise of the sheet, the entrance roller 19 and the exit roller 20 are arranged each in non-parallel relation with the length of the chamber in such manner that the sheet is passed obliquely through the chamber and thereby caused to shift lengthwise f the chamber. As shown in Fig, 2, the roller 1 9 is positioned at a small angle with the side walls and longitudinal axis of the chamber, its remote end being nearer the right hand side wall, and the roller 20 being parallel with the roller l9. As a result of these angular positions of the rollers i9 and 20, the lengths [2 of the strip extend obliquely crosswise of the chamber and the sheet takes a net oblique path in passing through the chamber as indicated by the dotted lines in Fig. 1. In other words, assuming that the strip is moving downward as viewed in the drawing, the lower exit end of the sheet, while parallel with the upper entrance end, is displaced toward the right hand longitudinally of the chamber. This displacement laterally of the strip in passing through the chamber is regulated by the angular relation of the rollers l9 and 20 with the side walls of the chamber. Preferably, this angular relation is such as to give a total displacement or shift of the sheet lengthwise of the chamber of substantially one-half of the length of the standing electromagnetic waves in the chamber. I nis assures that the strip at all crosswise points passes through the same values of field produced by the standing waves whereby it is heated uniformly.

In the modified form of our invention shown in Fig. 3, the two parallel sets of rollers 2| and 22 extend each horizontally across the chamber so that the lengths 23 of the strip 24 are vertical, as seen in the drawing, and parallel with the electric field indicated by the arrows. The rollers in this case must be made of a low loss dielectric material, such as polystyrene, low loss glass, etc.

This arrangement of Fig. 3 is especially effective in the heating of sheets or strips of thin dielectric material, such as very thin cellophane. The arrangement of the lengths of the sheet in parallel relation with the field component provides for an increased generation of heat in thin material as compared with the arrangement of Figs. 1 and 2, wherein the lengths are perpendicular to the field components. In a typical apparatus very thin cellophane was heated to a smoking temperature in about two seconds.

As applied to our invention we define ultra high frequency as a frequency of one megacycle or higher.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An ultra high frequency heater comprising Walls made of an electrically conducting material forming an elongated chamber, a high frequency supply source connected to said chamber for producing a transverse electric field mode in said chamber, two sets of rollers mounted in said chamber in spaced apart relation with each other transversely of said electric field a distance at least substantially one-half of the wave length in chamber whereby heating of said rollers is minimized, and two opposite walls of said chamber being provided each with an opening through which a sheet of material to be heated may be passed over said rollers back and forth between said sets of rollers in a plurality of lengths extending transversely of said chamber.

2. An ultra high frequency heater comprising walls made of an electrically conducting material forming an elongated chamber, a high frequency supply source connected to said chamber for producing transverse standing electromagnetic waves in said chamber, two sets of rollers mounted in said chamber in spaced relation with each other transversely of said chamber, two opposite walls of said chamber being provided each with an opening through which a sheet of material to be heated is passed over said rollers back and forth between said sets of rollers in a plurality of lengths extending transversely of said chamber, and means for guiding the sheet obliquely to said sets of rollers so as to cause the sheet to shift lengthwise of said chamber an amount at least substantially onehalf of the wave length in said chamber thereby to effect uniform heating of the sheet.

3. An ultra high frequency heater comprising walls made of an electrically conducting material forming an elongated chamber, a high frequency supply source connected to said chamber for producing transverse standing electromagnetic waves in said chamber, two sets of rollers mounted in said chamber in spaced relation with each other transversely of aid chamber, two opposite walls of said chamber each being provided with an opening through which a sheet of material to be heated is passed over said rollers back and forth between said sets of rollers in a plurality of lengths extending transversely of said chamber, and a guide roller in said chamber adjacent each of said opening extending at an acute angle with the longitudinal axis of said chamber for guiding the sheet obliquely to and from said sets of rollers so as to cause the sheet to shift along the longitudinal axis of said chamber an amount at least substantially one-half of the wave length in said chamber thereby to effect uniform heating of sheet.

HENRY EARL REVERCOMB. PHILIP VJ. MORSE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,197,122 Bowen Apr. 16, 194.0 2,291,807 Hart Aug. 4, 1942 2,364,526 Hansell Dec. 5, 1944 2,399,930 Keister May 7, 1946 OTHER REFERENCES Engineering Abstracts, Product Engineering, January, 1947, pages 137-140, particularly page 138.

Heating with Microwaves, Electronics, March, 1947, pages 82-85, particularly page 83. 

